Digital watches and clocks have become so commonplace that fully integrated clock circuits are widely available requiring little more than the connection of an external battery, a display and suitable set switches to construct a fully functional timepiece. Such integrated circuits are based on a highly accurate oscillator usually employing a quartz crystal and a counter. Suitable registers are connected to the counter and have respective outputs which are adapted to toggle after a predetermined number of pulses have been counted. In this manner, stock can be taken separately of the passage of seconds, minutes and hours. Likewise, after suitable initialization, track can be taken of the successive passage of twenty-four hour periods, thus allowing calendar data also to be maintained and displayed. The outputs are converted from binary-coded decimal format for display on 7-segment displays. Usually, an alarm clock function is also provided so as to alert the user of the watch at a preset time of day, typically so as to awaken the user from sleep.
Currently available digital watches, once set by the manufacturer or user, maintain an accurate record of the time and calendar data but take no account of the small seasonal changes in sunrise time which occur in any given location. Such changes occur continuously and, unless corrected for, are cumulative over a period of time. More specifically, sunrise occurs later throughout the winter until mid-winter and occurs earlier throughout the summer until mid-summer.
The cumulative change in sunrise time, over a period of time, results in an increasing seasonal discrepancy between the time of sunrise and the time a person must start the day. This is unpleasant because most people prefer to rise when it starts to get light outside. Thus, if this requirement is met at the start of winter, then owing to the increasing delay in time of sunrise throughout winter until the onset of mid-winter, people who rise at the same time each day will be constrained to do so when it is increasingly dark outside. On the other hand, in summer people tend naturally to awaken earlier than necessary owing to the increasing advance in time of sunrise throughout summer.
In many countries it is common to make a one-off correction for the cumulative delay and advance in sunrise time by "moving the clock" forward in summer and backward in winter, usually by one hour at a given time on a specified day at the start of summer and winter. Obviously, any day may be specified as to when the necessary correction or corrections should be made and this is usually determined by each government in an effort to make maximum use of available daylight, thereby reducing the need for artificial illumination and thereby saving energy. Such considerations may encourage seasonal corrections to be made more than once each season.
Regardless of how many times a season correction is made, it frequently plays havoc with the internal bio-clock of the workforce. The reason for this is obvious when the clock is moved forward in summer, because the adjustment is normally effected at midnight or in the middle of the night causing people to lose an hour's sleep. However, in the winter the adjustment is no less convenient for two reasons. First, people normally go to bed an hour later since they know that nominally they will have the same number of hours'sleep. Thus, at best, they receive no benefit from the hour gained. Usually, however, their body wakens at the normal time to which they have become accustomed which is now an hour earlier than necessary. So they lose on both counts and suffer from tiredness until their bodies become accustomed to the new regimen.
This inability to adjust to a sudden change in nominal time is due to the fact that, in order to be effective, a large increment of at least one hour, must either be added or subtracted from the nominal time once each season. The actual change in time of sunrise is, of course, much more gradual but it is not very practical to make many small adjustments throughout each season.
In addition to time changes caused by seasonal effects, it is also known that sunrise changes with longitude and this gives rise to geographic-dependent time changes according to one's longitude. Here, too, each adjacent time zone has a time difference of one hour, either plus or minus depending on the relative longitude of the adjacent zones. People who travel from one time zone to another must set their watches accordingly and the cumulative time difference in travelling between remote zones, and thereby crossing many intermediate time zones results in the phenomenon well-known as "jet lag" with its attendant exhaustion.
Whilst there is no way to compensate for jet lag, the patent literature has addressed the need to adjust one's watch when crossing adjacent geographic time zones. Thus, U.S. Pat. No. 3,827,233 in the name of Villar discloses a mechanical geographic timepiece wherein the minute hand is rotated, via a worm and bevel gear system in accordance with the inclination of the polar axis of the earth. This allows for automatic compensation for changing longitude as the timepiece is transported through different time zones.
U.S. Pat. No. 4,671,672 to Hubner discloses a universal time clock employing a globe which is driven by the hour tube of a left-hand rotating clockwork.
Both of these patents describe cumbersome mechanical clockwork systems for compensating for changes in longitude and are relevant only to the extent that such changes are also due to differences in time of sunrise. Neither of these references describes a portable timepiece which compensates for seasonal changes in time of sunrise in a fixed geographic location so as to enable a user or a community of users to operate according to time of sunrise.